In orthodontic treatment, tooth rotation, the movement of a tooth around its long axis, is considered to be one of the most difficult problems to solve. In order for an orthodontic archwire to exert an effective rotating force on a tooth, orthodontic brackets have evolved to include rotation wings. These rotation wings provide archwire contact points which are mesial and distal to the archwire slot and effectively increase the rotational force which can be exerted by an archwire on a tooth.
Rotation wing brackets developed to date include several all-metal brackets as well as a plastic bracket having metal rotation wings. The Lewis bracket and the Lang bracket are all-metal rotation wing brackets available in both weldable and bondable forms. Referring to FIG. 10, a bondable Lewis bracket is shown brazed to a foil mesh pad and available for bonding to a tooth. This particular bracket offers the orthodontist three potential archwire-contacting points for use in transferring a force from an archwire to a tooth. These three points include the two rotation wings as well as the center of the bottom wall of the archwire slot. However, because the Lewis bracket is brazed to a foil mesh pad, the braze rigidly bonds the rotation wings, thereby preventing adjustment of the rotation wings. Furthermore, the all-metal bracket does not offer the aesthetics of a bracket using non-metallic materials. The weldable version of the Lewis bracket does allow for some adjustment of the rotation wings because the bracket is welded to a band at a central point on the bracket and braze fill is not used. However, this option still offers limited aesthetic appeal.
The Lang bracket offers another rotation wing option in an all-metal weldable or bondable bracket. The rotation wings of this bracket are provided with no curvature and extend out from the archwire slot parallel with the bottom wall of the slot. In order for an orthodontist to adjust these rotation wings once the bracket is secured to a tooth and treatment is begun, the archwire must be removed from the bracket.
The Wick rotation wing bracket, a more recent development in an all-metal bondable bracket, offers several advantages over other all-metal rotation wing brackets. As can be seen in FIG. 11, although the body of the bracket is brazed to a foil mesh pad, the braze fill does not prevent adjustability of the rotation wings. Therefore, an orthodontist may achieve different degrees of rotational force without having to change the bracket on a particular tooth. Furthermore, because of the curvature of the rotation wings, an orthodontist may adjust the rotation wings once the bracket is on the tooth without having to remove the archwire. These advantages have made the Wick rotation wing bracket an attractive option when an all-metal bracket is desired.
Another option in the all-metal rotation wing bracket is the STYLE bracket sold by Ormco Corporation of Glendora, Calif. This single tie wing bracket offers the advantage of adjustable torque, The archwire slot and rotation wings are provided in a cylinder which may be rotated within the body housing to achieve the desired torque. Once the cylinder has been adjusted to the desired torque, it is brazed into place. The rotation wings of the STYLE bracket extend outwardly from the archwire slot along the same axis as the bottom wall of the slot. Therefore, if an orthodontist wishes to adjust either rotation wing once the bracket is positioned on a tooth, the orthodontic archwire must first be removed.
The use of rotation wings in an aesthetically pleasing plastic orthodontic bracket is taught by Reher et al. in U.S. Pat. No. 5,254,002. The '002 bracket is a translucent or transparent plastic bracket having a metal insert for reinforcing the archwire slot, thereby balancing the strength of an all-metal bracket with the aesthetically pleasing characteristics of a translucent or transparent plastic. The rotation wings on the '002 bracket extend straight out from the archwire slot parallel with the bottom wall of the slot. Therefore, when an archwire is placed in the archwire slot, an orthodontist is unable to adjust either rotation wing without first removing the orthodontic archwire. In addition, the metal insert of the '002 bracket has a mesial-distal wing span of about 0.14 in. from the outer end of one rotation wing to the outer end of the other rotation wing. This mesial-distal length is somewhat shorter than the mesial-distal length of the wings in several of the all-metal brackets. And although this reduced length places less stress on the metal insert within the plastic bracket, it also reduces the amount of rotational force which can be transferred from an orthodontic archwire to a tooth.
Therefore, it is desirable to have a single orthodontic bracket which provides both a highly aesthetically pleasing appearance and the ability to transfer significant rotational forces to a tooth. It also is desirable to have such an orthodontic bracket in which the rotation wings may be easily adjusted by an orthodontist without having to remove an archwire from the archwire slot.